<template>
  <div class="pagination">
    <!--上-->
    <button :disabled="pageNo===1" @click="$emit('pageNoClickCallback', pageNo - 1)">上一页</button>
    <button v-if="startNumAndEndNum.start > 1" @click="$emit('pageNoClickCallback', 1)" :class="{active:pageNo === 1}">1</button>
    <button v-if="startNumAndEndNum.start > 2">···</button>

    <!--中间部分-->
    <button v-if="page>=startNumAndEndNum.start" v-for="(page,index) in startNumAndEndNum.end" :key="index" @click="$emit('pageNoClickCallback', page)" :class="{active:pageNo === page}">
      {{page}}
    </button>

    <!--下-->
    <button v-if="startNumAndEndNum.end < totalPage - 1">···</button>
    <button v-if="startNumAndEndNum.end < totalPage" @click="$emit('pageNoClickCallback', totalPage)" :class="{active:pageNo === totalPage}">{{ totalPage }}</button>
    <button :disabled="pageNo===totalPage" @click="$emit('pageNoClickCallback', pageNo + 1)">下一页</button>
    <button style="margin-left: 30px">共 {{ total }} 条</button>
  </div>
</template>

<script>
export default {
  name: "Pagination",
  props: ["pageNo", "pageSize", "total", "continues"],
  computed: {
    //总共多少页
    totalPage() {
      return Math.ceil(this.total / this.pageSize)
    },
    //计算出连续的页码，起始与结束
    startNumAndEndNum() {
      const {continues, pageNo, totalPage} = this
      let start = 0
      let end = 0
      //连续区间大于总页数，有多少页显示多少
      if (continues > totalPage) {
        start = 1
        end = totalPage
      } else {
        //连续区间小于总页数，只显示中间一部分，[-2,+2]或[-3,+3]
        start = pageNo - parseInt(continues / 2)
        end = pageNo + parseInt(continues / 2)
        //修正起始页
        if (start < 1) {
          start = 1
          end = continues
        }
        //修正结束页
        if (end > totalPage) {
          end = totalPage
          start = totalPage - continues + 1
        }
      }
      return {start, end}
    }
  }
}
</script>

<style lang="less" scoped>
.pagination {
  text-align: center;

  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
</style>
